1. Field of the Invention
The present invention relates to a vacuum processing system into which a wafer cassette, which holds a plurality of wafers to be treated, is fed and another wafer cassette into which treated wafers are put is taken out.
2. Description of the Related Art
In a vacuum processing system, such as dry etching system, CVD system, sputtering system and the like, in general, the operation is as follows: A predetermined number of wafers to be treated are held in a wafer cassette as a single unit (generally called a lot), the wafer cassette which holds the wafers is introduced into the system, and another wafer cassette into which the predetermined number of treated wafers are put is taken out, thus attaining high production efficiency.
One example of the conventional vacuum processing systems is shown in Japanese Patent Unexamined Publication No. 60-74531. In this system, the wafer cassette is placed on the table in the atmosphere, and the loading chamber is brought to atmospheric pressure. A first isolating valve between the loading chamber and the table is opened and a cassette drive unit and a wafer carrier cooperate with each other so that the first wafer to be treated, which is held in the lowest stage of the wafer loading cassette, is fed into the loading chamber. After the first isolating valve is closed and the loading chamber is evacuated, the second isolating valve provided between the loading chamber and a wafer processing chamber is .opened, and thus the loading chamber is communicated with the wafer processing chamber. The wafer is moved into the wafer processing chamber, and the second isolating valve is closed so that the desired treatment is performed on the wafer. During this treatment, the loading chamber is returned to atmospheric pressure again and the second wafer to be treated, which is held in the second stage from the bottom of the wafer loading cassette, is fed into the loading chamber. When the treatment of the first wafer is completed, the first wafer is fed into an unloading chamber and the second wafer is fed into the wafer processing chamber. While the second wafer is being treated, the first wafer is put into the uppermost stage of the wafer unloading cassette via the unloading chamber which has been returned to the atmospheric pressure. Other wafers are also treated one by one in the same manner. After the last wafer has been put into the wafer unloading cassette, the wafer unloading cassette is taken out.
The arrangement, however, may be modified when occasion demands such that the wafer is directly fed into the vacuum processing chamber without being passed through the loading chamber. An example of such a modified vacuum processing system is shown in Japanese Patent Unexamined Publication No. 55-162231.
A carrying unit shown, for example, in Japanese Patent Unexamined Publication No. 63-273331 is proposed in that it is designed to prevent contamination from generating due to dust, etc. which is stuck to wafers and a wafer cassette at the time that the wafers are carried into a semiconductor production process. In a wafer treatment of this example, when the wafers are carried out from the cassette and are put into the cassette, the cassette stage, on which the cassette is set, is fixed, while a carrying arm is provided in such a manner that it can be moved upwardly, downwardly, rotationally, or straightforwardly. At the same time, the drive portion is held inside the cover to comply with the above-described demands.
Another example of the system of the related arts is shown in Japanese Patent Unexamined Publication No. 63-211645. In this example, the cassette is fixed and a mechanism, in which two carrying arms formed on the upper and lower stage are moved upwardly and downwardly, is employed so that the generation of contamination due to dust, etc. can be prevented. At the same time, the carrying arms can access the wafer in the cassette randomly and each of the treated wafers can be fed back to the original position where one of the wafers to be treated was held.